The present invention relates to a process unit which can be applied to, for example, a copy machine, a facsimile machine or a printer.
Process units of the above-described type each include a photosensitive drum. The surface of the photosensitive drum is charged with an electric charger, and then a laser beam corresponding to image data is irradiated onto the surface of the thus-charged photosensitive drum, thereby forming an electrostatic latent image. After that, toner is supplied onto the static latent image with a developer roller so as to form a toner image, which is then transferred onto a recording material such as a paper sheet. Toner remaining on the photosensitive drum is removed with a drum cleaner and collected.
The above-described photosensitive drum, electric charger and drum cleaner are held in a casing, which forms a drum unit, and the developer roller is held in another casing, which forms a developer unit.
Both side surface portions of each of the drum unit and developer unit are held with side surface covers, and a lower end portion of each of these side surface covers is fixed by screws to the bottom plate frame. Further, a back surface side of the drum unit is covered by a back surface cover.
Here, the side surface covers of the drum unit and developer unit are each designed to have such a structure that each cover can be divided into two to the drum unit side and developer unit side, for the purpose of improving ease of maintenance. When assembling the drum unit and developer unit, first, the drum unit is aligned with the developing unit, and then the side surface covers of the drum unit are fixed.
However, in a conventional unit, the position where the drum unit is aligned is different from the position where the drum unit is fixed. With this structure, even after the drum unit is positioned, it is sometimes displaced from the position when it is actually fixed. Therefore, the accuracy of the alignment is low.
In the meantime, the electric charger has a hook on each of its end portions, and each hook is engaged with the casing of the drum unit or a bearing portion located between the casing and the photosensitive drum. Thus, the charger is held and at the same time is aligned at the appropriate position.
Further, one end of the photosensitive drum is supported rotatably by one side surface portion of the casing via the bearing, whereas the other end is held rotatably by the other side surface portion of the casing via a holder which serves also as a bearing.
Moreover, the drum cleaner is supported by both its end portions on both side surface portions of the casing via support pins.
On the other hand, in a conventional apparatus, the hooks of the electric charger, the bearing holder of the photosensitive drum, and the support pins for the drum cleaner are provided on an inner side of the side surface cover. Due to such a structure, for maintenance for the electric charger, it is necessary to remove the side surface cover of the drum unit to disengage the hook and then remove the back surface cover so as to dismount the electric charger. The side surface covers also serve to hold the gears of the drum mechanism and the connection between the developer unit and the drum unit. With this structure, these units and parts such as gears must be dismounted when the side surface covers are removed, which is laborious.
Further, for maintenance of the photosensitive drum and drum cleaner, the side surface covers of the drum unit must be taken off after separating the drum unit and developer unit from each other, and then the photosensitive drum and drum cleaner must be dismounted by removing the holders and support pins, which is laborious as well.
As described above, the conventional technique entails such a drawback that it is very laborious to dismount the electrical charger, photosensitive drum or drum cleaner. Due to this drawback, at the end of the lifetime of the photosensitive drum, the entire drum unit must be, in many cases, discarded and replaced with a new unit. The life of the photosensitive drum is as long as or shorter than that of the electrical charger, and therefore it is very wasteful to replace the entire unit when only the drum needs replacing.
Apart from the above, conventionally, when spent drum units collected from users are to be subjected to maintenance or recycled, a great number of maintenance steps are required, thereby making it difficult to recycle them.